The following table categorizes methods of detecting an analyte. As you can see, using electromagnetic radiation (spectroscopy) is one of a very limited number of general stategies for detecting an analyte.
| Physical properties mass refractive index thermal conductivity | With electromagnetic radiation absorption emission scattering | By an electric charge (or current) electrochemistry mass spectrometry |
Physical methods tend to be very general but are not as sensitive as instrumental methods that use spectroscopy or charge detection. Keep in mind that there are a large number of specific analytical techniques in each of these categories. But the above example does put analytical spectroscopy techniques in perspective.